In the manufacture of semiconductor devices and further products, ion implantation systems are used to impart dopant elements into semiconductor wafers, display panels, glass substrates, and the like. Typical ion implantation systems or ion implanters implant a workpiece with an ion beam of impurities in order to produce n-type and/or p-type doped regions, or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects a selected ion species into the workpiece to produce the desired extrinsic material properties. Typically, dopant atoms or molecules are ionized and isolated, accelerated and/or decelerated, formed into a beam, and implanted into a wafer. The dopant ions physically bombard and enter the surface of the wafer, and subsequently come to rest below the wafer surface.
A typical ion implantation system is generally a collection of sophisticated subsystems, wherein each subsystem performs a specific action on the dopant ions. Dopant elements can be introduced in gas form (e.g., a process gas) or in a solid form that is subsequently vaporized, wherein the dopant elements are positioned inside an ionization chamber and ionized by a suitable ionization process. For example, the ionization chamber is maintained at a low pressure (e.g., a vacuum), wherein a filament, for example is located within the chamber and heated to a point where electrons are emitted from the filament. Negatively-charged electrons from the filament are then attracted to an oppositely-charged anode within the chamber, wherein during the travel from the filament to the anode, the electrons collide with the dopant source elements (e.g., molecules or atoms) and create a plurality of positively charged ions from the source elements. The positively charged ions are subsequently “extracted” from the chamber through an extraction slit via an extraction electrode, wherein the ions are generally directed along an ion beam path toward the wafer.
Typically, a single mode ion source is utilized within an ion implantation system to generate ions of various differing dopant ion species, wherein a change in species (e.g., a change from a first species or process gas to a second reactive species or process cleaning gas) is necessitated in order to perform the specific ion implantations and cleaning of the implantation system. One drawback to using a single mode ion source for implanting various species of ions is that at times it is desirable that the ion source be operated at low density, and therefore low power in order to prevent disassociation of the large molecules utilized within the ion source. Substantial improvements in throughput have been demonstrated for low energy boron implants, for example using large charged ions such as decaborane and octadecaborane. However, at other times, it is desirable to be able to run the ion source at a much higher power in order to run standard implantation gases such as boron trifluoride (BF3), phosphine (PH3) and arsine (AsH3). Thus standard implantation gases are often run at much higher source temperatures. Ion source design for both areas of operation has proven to be problematic.
In addition, it has been found that periodic source cleaning with reactive species such as fluorine is necessary when operating large molecule gases such as decaborane and octadecaborane. Present technology typically uses an external fluorine generator, adding considerable cost and complexity to the system. The external fluorine systems can introduce problems, for example process variability, reduced yields, flow rate issues, and the like.
Accordingly, a need currently exists for a more efficient ion source and apparatus, wherein the ion source can operate in various modes in order to meet more of the needs within the ion implantation industry.